textproduct: Rapid City

KEY MESSAGES

- Showers move out today. Highest rainfall amounts over northwestern South Dakota.

- Period of gusty winds around 50mph just east of the Black Hills today.

- Mild Saturday. Chance of afternoon showers and thunderstorms over the Black Hills.

- Warmer beginning on Sunday and continuing through next week.

UPDATE

Issued at 1158 PM MDT Thu May 21 2026

Upper low spinning over east-central WY per water vapour will lift northeast this morning, taking associated compact surface low with it. Narrow band of stronger winds expected in the squeeze areas just east of the Black Hills. Forecast sounding momentum transfer suggests a few gusts to 45kts possible with latest MOS guidance in the ballpark. Probabilistic guidance indicates a 50-90% chance of 50mph wind gusts for the same areas. Have hoisted a Wind Advisory to account.

UPDATE Issued at 938 PM MDT Thu May 21 2026

Upper low and associated rain and isolated ts will continue to shift east across the region through Friday. Rain will expand in coverage across western SD tonight as the main area of lift spreads over the region. Instability has waned significantly, hence not expecting more that a few isolated thunderstorms through the night toward central SD. Gusty NW winds will develop Fri morning, esp across the SD Plains where gusts will approach 50 mph for a brief period Fri morning in the lee of the Black Hills. Things dry out and cool off Fri night, with some frost possible across northeast WY. Residual cyclonic flow coupled with sufficient moisture and steep lapse rates over the BH may support a few showers there Sat afternoon. Otherwise, much warmer and drier to start next week, with increasingly unsettled weather later next week as a trough moves into the Rockies with SE LL flow over the Plains.

DISCUSSION

(This Evening Through Thursday) Issued at 1248 PM MDT Thu May 21 2026

Upper level analysis has an area of low pressure centered over western Saskatchewan and a trough extending down the east side of the Rockies to the Four-Corners area. At the surface, a stationary boundary extends through the western Dakotas into southeastern Wyoming. Showers and thunderstorms have already begun to pop over the northern Black Hills, and expect coverage to increase this afternoon along the frontal boundary as the upper level trough moves toward the forecast area. CAPE is around 500 J/kg, thus a few stronger storms capable of producing gusty winds and hail are possible this afternoon.

Expect showers/isolated thunderstorms to overspread the entire forecast area tonight before ending from west to east on Friday. Lower end/25th percentile precipitation accums are 0.1" to 0.2" across northeastern Wyoming and southwestern South Dakota upward to 3/4" to an inch across northwestern South Dakota and the northern Black Hills. Higher end/75th percentile are up to 1.75" across northwestern South Dakota.

As the system moves out on Friday, breezy northwest winds are expected, especially across the South Dakota Plains where gusts around 45 mph are possible for a few hours late Friday morning. Sustained winds should average around 25 mph. With winds on the low end of advisory criteria, have decided against any wind highlights at this time.

Temperatures on Saturday will begin to warm up, with highs in the mid 60s to mid 70s. Residual cold pool aloft and lingering low-level moisture could support isolated showers over the Black Hills in the afternoon.

The warming trend begins on Sunday as the western upper ridge builds. Above normal highs in the mid 70s to upper 80s will return with even warmer conditions on Memorial Day. The upper flow turns more south-southwesterly on Tuesday and the area remains in south- southwesterly flow through the end of the week. This will likely allow for moisture to advect into the area and could be the start of the severe weather season - which is typical for this time of year.

AVIATION

(For the 12Z TAFS Through 12Z Saturday Morning) Issued At 519 AM MDT Fri May 22 2026

Departing upper low will push a large area of rain (snow up high) northeast today over western SD and extreme northeastern WY. Widespread MVFR/IFR conditions are expected in the precipitation. Conditions will slowly improve after the precipitation ends with mostly VFR by tonight. Gusty northwest winds will develop this morning, especially just east of the Black Hills where gusts to 45kts are likely into the early afternoon hours.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Wind Advisory until 3 PM MDT this afternoon for SDZ013-030-031- 042-073. WY...None.